{
  "slug": "effective-capacity",
  "term": "Effective capacity",
  "aliases": [],
  "definition": "Effective capacity, under the SNIA convention, combines stored logical data with remaining formatted capacity.",
  "note": "Accounting: Space optimization can let the logical data represented exceed its physical footprint. The SNIA measure adds that stored data to unused formatted capacity; it does not assume the unused part will achieve the current reduction ratio. [snia-effective]\n\nForecast: Multiplying total usable capacity by an observed reduction ratio is a different, conditional estimate. Future data and retained versions can change the ratio. Neither figure is a reservation of backing space. Product counters require their own documented accounting scope. [snia-effective] [ontap-capacity]\n\nPlanning: Keep current accounting separate from a future-workload budget and from policy headroom. In a hypothetical pool with 60 TB logical stored in 30 TB and 70 TB free, leaving 10 TB unused gives a 60 TB physical growth budget. An incoming 1.6:1 mix adds 96 TB logical, versus 120 TB at the old 2:1 ratio under the same headroom. The policy is not an enforced reservation. After that modeled addition, the new SNIA snapshot is 156 + 10 = 166 TB, not the original 130 TB.",
  "status": "unknown",
  "advantages": [],
  "limitations": [],
  "related": [
    "raw-capacity",
    "usable-capacity",
    "data-reduction-ratio",
    "thin-provisioning"
  ],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "citations": [
    {
      "id": "snia-effective",
      "title": "SNIA Dictionary: effective capacity",
      "url": "https://www.snia.org/education/online-dictionary/term/effective-capacity",
      "accessed": "2026-10-22"
    },
    {
      "id": "ontap-capacity",
      "title": "NetApp ONTAP: capacity reporting and measurements",
      "url": "https://docs.netapp.com/us-en/ontap/concepts/capacity-measurements.html",
      "accessed": "2026-10-22"
    }
  ],
  "updated": "2026-10-23",
  "provenance": [
    "Terminology follows the cited accounting convention; no storage-array measurement or capacity guarantee is implied."
  ]
}